Harmful components, such as nitrogen oxides, carbon monoxide and hydrocarbons, are contained in exhaust gas discharged from internal combustion engines, etc. Various kinds of devices have been developed conventionally to eliminate such substances from the exhaust gas thereby to purify the exhaust gas.
The applicant of the present invention developed an exhaust gas purification device and has already applied for a patent (Patent document 1). FIG. 4 shows an exhaust gas purification device shown in FIG. 1 of Patent document 1. As shown in FIG. 4, in the conventional exhaust gas purification device proposed by the applicant, a nitrogen oxide adsorbing material 204, a first combustion device (adsorbed material detachment unit) 203 and a second combustion device 205 are provided for each of a plurality of branch exhaust passages 202a and 202b connected to an internal combustion engine or the like. The exhaust gas discharged from the internal combustion engine or the like. is supplied only to one of the branch exhaust passages, i.e., 202a (or 202b), and not supplied to the other branch exhaust passage 202b (or 202a). Furthermore, in the branch exhaust passage 202a to which the exhaust gas is supplied, nitrogen oxides are adsorbed onto the nitrogen oxide adsorbing material 204 and eliminated, and carbon monoxide and hydrocarbons are oxidized to carbon dioxide and water by the oxidation catalyst contained in the nitrogen oxide adsorbing material 204. On the other hand, in the branch exhaust passage 202b to which the supply of the exhaust gas is shut off, nitrogen oxides are detached from the nitrogen oxide adsorbing material 204 since the first combustion device 203 generates a reducing atmosphere, and the detached nitrogen oxides are reduced to nitrogen by the combustion device 205. In other words, normal operation in which nitrogen oxides are adsorbed onto the nitrogen oxide adsorbing material 204 is performed in the one branch exhaust passage 202a. At the same time, in the other branch exhaust passage 202b, regeneration operation in which nitrogen oxides are detached from the adsorbed material detachment unit 204 is performed. As a result, the adsorption capability of the nitrogen oxide adsorbing material 204 is maintained.
The exhaust gas purification device shown in FIG. 4 is a purification device that does not use a three-way catalyst, ammonia, urea, etc. The three-way catalyst serving as a catalyst capable of decomposing nitrogen oxides, carbon monoxide and hydrocarbons simultaneously does not act effectively in an excess air condition. In the case of a purification device that uses ammonia, etc., the device itself is very complicated and expensive. In addition, maintenance cost is necessary for ammonia, etc. serving reducing agents, and it is necessary to provide a system for supplying ammonia, etc., whereby many problems occur. In the exhaust gas purification device shown in FIG. 4, these problems have been solved. The exhaust gas purification device shown in FIG. 4 can eliminate harmful components (nitrogen oxides, carbon monoxide and hydrocarbons) from the exhaust gas discharged from an internal combustion engine or the like operating in an excess air condition to purify the exhaust gas and can maintain its purification capability without lowering the capability.
Patent document 1: Japanese Patent Application Laid-open Publication No. 2006-272115